Methods and apparatus for precharge monitoring of high voltage circuits

Abstract

Methods and apparatus to monitor the precharging of high voltage circuits are disclosed. In one embodiment, an apparatus includes a switch that selectively enables or disables precharge current to a high voltage circuit based on a switch control signal. The apparatus also includes a comparison circuit that compares a scaled version of a circuit voltage to a reference voltage to generate the switch control signal. In one embodiment, the switch control signal is generated to enable the precharge current when the scaled version of the circuit voltage is greater than the reference voltage.

What is claimed is: 
     
       1. An apparatus comprising:
 a precharge switch that selectively enables or disables precharge current from a Direct Current (DC) source to a capacitor; 
 a comparison circuit that generates a switch control signal to continuously control the precharge switch, wherein the switch control signal is generated based on a comparison between a scaled version of a circuit voltage and a reference voltage; and 
 a reference circuit that receives a precharge command signal and generates the reference voltage, wherein the precharge switch changes state in response to the precharge command signal changing state. 
 
     
     
       2. The apparatus of  claim 1 , further comprising:
 a resistor connected in series with the precharge switch, wherein both the resistor and the precharge switch are connected between a high voltage supply and the capacitor, and wherein the high voltage supply outputs a voltage of at least 400 volts. 
 
     
     
       3. The apparatus of  claim 2 , wherein the resistor is configured to generate a selected amount of current as the precharge current. 
     
     
       4. The apparatus of  claim 1 , wherein the precharge command signal is a PCH ENABLE precharge command signal. 
     
     
       5. The apparatus of  claim 4 , wherein the reference circuit comprises an RC circuit that receives the PCH ENABLE precharge command signal and generates the reference voltage. 
     
     
       6. The apparatus of  claim 4 , further comprising:
 a controller that generates the PCH ENABLE precharge command signal. 
 
     
     
       7. The apparatus of  claim 1 , wherein the comparison circuit generates the switch control signal to control the precharge switch to enable the precharge current to the capacitor it when the scaled version of the circuit voltage is greater than the reference voltage. 
     
     
       8. The apparatus of  claim 7 , wherein the comparison circuit comprises:
 a comparator that receives the reference voltage at a negative input terminal and receives the scaled version of the circuit voltage at a positive input terminal and generates a comparison voltage at an output terminal; and 
 a logic AND gate that receives the comparison voltage and a precharge command signal and generates the switch control signal. 
 
     
     
       9. The apparatus of  claim 1 , further comprising:
 a voltage generator that receives and scales the circuit voltage to generate the scaled version of the circuit voltage. 
 
     
     
       10. The apparatus of  claim 9 , wherein the voltage generator comprises:
 a resistor network that forms a voltage divider that receives the circuit voltage and generates the scaled version of the circuit voltage which shares a voltage reference point with the reference voltage. 
 
     
     
       11. The apparatus of  claim 9 , wherein the voltage generator comprises:
 a resistor network that forms a voltage divider that receives the circuit voltage and generates a divided voltage which shares a voltage reference point with the reference voltage; and 
 an amplifier that receives the divided voltage and adjusts for scale and offset to generate the scaled version of the circuit voltage. 
 
     
     
       12. The apparatus of  claim 1 , further comprising:
 a main switch coupled between the DC source and the capacitor, wherein the main switch is controllable independently from the precharge switch. 
 
     
     
       13. A method comprising:
 selectively enabling or disabling precharge current from a Direct Current (DC) source to a capacitor based on a switch control signal; and 
 comparing a scaled version of a circuit voltage to a reference voltage to generate the switch control signal, wherein the comparing is performed non-discretely during precharge, wherein the reference voltage is generated from a precharge command signal, and wherein the switch control signal changes state in response to the precharge command signal changing state. 
 
     
     
       14. The method of  claim 13 , further comprising:
 generating a selected amount of current for use as the precharge current. 
 
     
     
       15. The method of  claim 13 , wherein the the reference voltage is generated using an RC circuit that receives the precharge command signal. 
     
     
       16. The method of  claim 12 , further comprising:
 generating the precharge command signal using a controller. 
 
     
     
       17. The method of  claim 12 , further comprising
 receiving and scaling the circuit voltage to generate the scaled version of the circuit voltage. 
 
     
     
       18. The method of  claim 12 , wherein the operation of comparing comprises:
 dividing the circuit voltage to generate a divided voltage; and 
 referencing the divided voltage to a voltage reference point to generate the scaled version of the circuit voltage, wherein the reference voltage is also referenced to the voltage reference point. 
 
     
     
       19. The method of  claim 12 , wherein the operation of comparing comprises:
 comparing the reference voltage to the scaled version of the circuit voltage to generate a comparison voltage; and 
 performing a logic AND function with the comparison voltage and the precharge command signal to generate the switch control signal. 
 
     
     
       20. The method of  claim 13 , wherein the switch control signal controls a precharge switch, wherein a main switch is coupled between the DC source and the capacitor, and wherein the main switch is controllable independently from the precharge switch. 
     
     
       21. An apparatus comprising:
 a switch that controls precharge current from a Direct Current (DC) source to a capacitor; and 
 means for enabling and disabling the switch by continually comparing a scaled circuit voltage and a reference voltage wherein the reference voltage is generated from a precharge command signal, and wherein the switch changes state in response to the precharge command signal changing state. 
 
     
     
       22. The apparatus of  claim 21 , wherein the means is a precharge monitoring circuit. 
     
     
       23. The apparatus of  claim 21 , wherein a main switch is coupled between the DC source and the capacitor, and wherein the main switch is controllable independently from the switch that controls precharge current.